Control of power absorbed in electric furnaces



Paten t d Jan. 6, 1920.

APPLICATION FILED APR.24, 1919.

CIC. GOW AND D. F. CAMPBELL. CONTROL OF POWER ABSORBED IN ELECTRIC FURNACES.

C. C. 60W AND D. F. CAMPBELL. CONTROL OF POWER ABSORBED m ELECTRIC FURNACES.

APPLICATION FILED APR.24, 919.. 1,327,548, Patented. Jan. v6, 1920.

2 SHEETS-SHEET 2.

ways?" 1 UNITED? STATES: PATENT mm;

COLIN CLARENCE GOW AND DONALD FIBiASER CAMYBELL, OF LONDON ENGLAND.

common or rowan Ansonnnn IN nnnc'mic FURNACES.

1,32%548. Peciflcetlon of Letters Patent. I V Patented Jain. 6,1920- Application filed April 24, 1919. Serial 30.292338. v f

To all whom it may concern: ance' in the latter case being inserted in or- Be it known that we, Conm CLARENCE der to obtain a hand regulation. The pres- Gow and DONALD Fnasnn CAMPBELL, both ent invention relates to this type of apparasub ects of the King of Great Britain, retus and consists in improvements by which 5 siding in London, England, have jointly in the fluid pressure supply is controlled by an vented certain new and useful Im roveindependent source of electricity, the cur 6 ments Relating to the Control of ower rent strength of which is varied in corre-- Absorbed in Electric Furnaces, of which the spondence with the load.

following is a specification. Also means are provided by which the in This invention relates to the control of predetermined load can be varied within power supplied to electric furnaces in which wide'liinits. It is usually necessary, during the power absorbed is entirely or in part some phase of an electric furnace process,

dependent upon the position of movable more especially in the manufacture of steel,-

conductors hereinafter called electrodes. to maintain the current at one fourth or It is known to maintain the power supeven less of its full load value and to effect plied to furnaces of this type at any-prethe automatic regulation with small limits,

determined value by gearing, operated elsefor example, of about 5 per cent. If the 'trically or by hand, which actuates the elecfurnace is supplied with alternating curtrodes in the direction either to increase or rents, in order to obtain the necessary )ower 20 diminishthe resistance ,to the passage of the for operating the solenoid or other device electric current. The gearing, when elecwhich controls by means of the variable trically operated, is actuated by reversible resistance, the strength of the current in the motors which are connected either by handindependent circuit, it is convenient to proor by automatically controlled apparatus vide tappings from the secondary circuit as with an independent source of electric. of the current transformer, so that the supply. stren h of the secondary circuitis approxi- The motors if automatically controlled mate y constant for difierent values of the are usually energized intermittently, and primary current. A current transformer is impart corresponding movements to the provided in the circuit of a single phase as electrodes until the required adjustment has system or in each phase of a polyphase sysbeen made. m. p

If a considerable movement. is necessa Y In electric furnaces in which the current before the normal conditions are obtaine passes in series through two or more electhe installation may be working for some trodes, or in polyphase alternating circuits,

35 appreciable time "under unfavorable condiin order that the voltage should be divided tions and, on the other hand, if the fiuctuaequally between the electrodes, the electrotions to be controlled are of small extent, magnetic devices controlling the current the correction applied may be in excess offrom the independent source are energized the requirements and oscillating movements by a winding of which the current depends to causing hunting of the regulating apon the voltage .between the electrodes and paratus may easily take place. the chargeas well as by a winding of which It is obvious that a better regulation the current depends upon the load. would be aiforded by a continuous move- A rectifier may be introduced to rect fy.

merit of the electrode in the required diiecthe current in the windings in the solenoid 45 tion, more especially if the .speed of the controlling the variable resistance. If the movement varied according to the extent of furnace power supply, is from a direct cur-, the adjustment required. rent source the solenoidcontrolling the vari- For this purpose it has been previously able resistance'may bepergized by a windproposed to move the electrode by means of ing connected acrossvthe terminals of a low 50 a supply of ressure fluid controlled by a resistance inserted mthe mam leads.

valve operate by an electromagnetic device The accompanying drawings show diaenergized b a current obtained from a curgrammatically, by way of example, circuit Y rent trans ormer in the load circuit, or arrangements accordmg to the invention.

shunted from that-circuit, variabie resist- In'the arrangement shown inFigure '1, a

solenoid is energized by a current transfformer inserted in the load circuit and automatically controls the movableelectrode by regulating the strength of the current from a This current load circuit; Fig. 5 shows a similar modification adapted for a three phase alternating current circuit.

The circuitssliown in Figs. 3, 4 and 5 are given as examples and may be suitably modified for other arrangements of the electrodes.

Referring to Fig. 1, 1 is a current transformer, preferably of the shell type, the primary winding 2 being traversed by the whole or a constant proportion of the main current supplied to the movable-electrode 4. The secondary winding 3 of the transformer energizes an electromagnetic device, shown in the example as a solenoid 5 of which the plunger 6 is drawn to the left against the action of a spring 7 in dependence on the strength of the current.

The plunger 6 controls by a resistance 8 the current strength in a circuit energized from an independent source of preferably direct current, represented in the example shown by a battery 9. This circuit includes a solenoid 10 the plunger 11 of which is connected with the stem 12 of a valve 13, which in its normal positioncloses both an inlet 1 1 to a supply of fluid pressure, such as oil, water or compressed air, and also a discharge outlet 15. If the current in the transformer 1 rises above the predetermined value, the plunger 6 of solenoid 5 is moved to the left and thereby increases the resistance 8, the solenoid '10 is less strongly energized and the valve 13 is moved to the left by a spring 16 to open the inlet 14- and supply fluid pressure through a pipe '17 to a cylinder 18 and thereby raise a piston 19 and with it the movable electrode 4.

If, on the other hand, the current in the circuit of the transformer 1, 2 falls below the predetermined value, the resistance 8 is lessened and the valve 13 is moved by the plunger 11 to the right, the inlet 14 remains closed and the fluid in the cylinder 18 is exhausted through the outlet 15, the piston 19 descending by the weight of the electrode, or the action of a spring or other suitable force.

A variable resistance 21 is connected in manually controlled in the requireddirection independently of the current 'in the transformer 3.

The resistance 8 might be connected in series instead of in parallel with the resistance 21.

It is not necessary that the plunger 11 of the solenoid 10 should be directly connectml with the spindle 12 of the valve 13; the movement of the plunger in either direction may be adapted to complete the circuit of a relay which effects the required operation of the valve and in this case is automatically brought into the normal position under spring control.

For the purpose of adjusting within wide limits the predetern'iincd value at which the load is to be maintained, tappings are connected with the secondary winding of the transformer 3 and led in the usual manner to contact studs 24-3l wiped by an arm 32 which conveys current to one terminal of the solenoid 5. In this case the resistance 21 is only required for the hand control of the electrodes.

Although it has been assumed that a single valve may be used to control the supply of fluid pressure, it is obvious that a combination of valves may be used for this" purpose;

In the arrangement shown in Fig. 3 in which the electrodes 4 and 4" are connected in series over the leads a and b of a single phase alternating circuit, the solenoid 5 is. energized by a winding in series with the secondary circuit 3 of the current transformer as in Fig. 1, and also by a winding 23 connected with the lead a and a point do in the cpnductin hearth.

Similarly, a so enoid 5 is energized by a winding connected with the secondary wind ing 3 of the current transformer and a winding 23 connected with the lead I) and the point This arrangement insures that an equal amount of power is absorbed between each electrode and the point a: and that the total power supplied is automatically maintained at the predetermined value.

In the arrangement shown in Fig. 1, the electrodes 4 and 1" are connected in series with a source of direct current over the leads a, 7). The solenoid 5 is energized by of the windings connected with the current transformers 3, 3", 3, and the windings 23, 23 23 connected res ectively With the leads a, b, a and with t e common junction 00.

In an installation provided With a su ply at constant current each electrode Won... d be automatically controlled in dependence on the voltage at the terminals of'the electrade.

Having thus described the natureof the said invention and the best means We know of carrying the same into practical efi'ect,

we cl aim sorbed in an electric furnace at Y of the furnace.

noid or other equivalent device. energized by the secondary Winding of a transformer of which the primary Winding is traversed by the current, or by a portion of the current, supplied to the electrodes of the furnace.

3. In control apparatus according to claim 1, means for automatically adjusting the variable resistances, comprising a solenoid or other equivalent device connected in parallel across a low resistance traversed bythe load current supplied to the electrodes .the automatically adjusted variable resistances referred to in claim 1, other resistances adapted to be' operated manuall Y predetermined va no of the current maintained in the movable electrode.

5. For-{the purpose of adjusting the predetermined value of the power supplied to the electric furnace, tappings taken from the secondary windings of the current transformer to the solenoid claimed in claim 2.

6. Control apparatus'according to claim 2, in which the solenoid or other equivalent device therein claimed is'provided-with an additional Winding energized by a current dependent upon the voltage between the electrode and the charge;

' 4. In parallel with In testimony whereof We have signedour names to this specification COLIN CLARENCE GOW. DONALD FRASER CAMPBELL.

in order to adjust the 

